The State could be obliged to provide consular assistance to an Irish citizen who is an Oxford-based academic accused by the US of being the leader in Britain of Palestinian Islamic Jihad, the militant organisation.
Mr Nasir Musa Mohammed Nafi has been an Irish citizen since 1994 when he exercised an automatic entitlement under now-defunct rules which guaranteed citizenship to the spouses of Irish people.
Although his wife, Ms Imelda Nafi (née Ryan), was born in Manchester, she is believed to be an Irish citizen, entitling her husband to exercise the entitlement.
The Department of Foreign Affairs is obliged under citizenship rules to ensure fair treatment of all Irish citizens should they be detained abroad.
Mr Nafi said yesterday that he had lived in Britain for 20 years, but had held passports from Ireland and Egypt, where he was born. He was shocked at the allegations against him, which he said were "baseless".
A professor of Islamic studies at Birkbeck College in London, he was indicted on racketeering charges by the US Justice Department on Thursday, with eight other alleged members of Islamic Jihad.
While the British Home Office is not believed to have received any request from the US in relation to Mr Nafi, he is thought to be under threat of extradition.
Mr Nafi and his wife have denied that he has had any involvement with the group, which is designated a terrorist organisation by the US and believed to be responsible for more than 100 deaths and suicide attacks in the Middle East.
The 120-page indictment, which was published by the US Attorney General, Mr John Ashcroft, said Mr Nafi was a founder of the Islamic Jihad, a member of its governing Shura council and leader of the organisation in Britain.
It indicates that Mr Nafi had come to the attention of the US authorities in 1988. This was six years before he became an Irish citizen, The indictment said defendants were members or associates of Islamic Jihad "at all times material to this indictment".
Islamic Jihad was described as "a criminal organisation whose members and associates engaged in acts of violence including murder, extortion, money laundering, fraud and misuse of visas, and operated worldwide".
The Department of Justice and Equality said it was unable to comment on individual cases when asked whether it Mr Nafi had come to its attention in 1994.
A Garda spokesman also said he could not comment on an individual case when asked whether he had been investigated.
The granting of citizenship to Irish residents is at the absolute discretion of the Minister for Justice, who must ensure that the individual concerned is a suitable candidate for naturalisation. Details of individuals who are naturalised must be published in Iris Oifigiúil.
It is believed that Mr Nafi's name has never been published in Iris Oifigiúil.
Under the post-nuptial rule, which ceased to apply last year, the only tests which applied to Mr Nafi were whether he had been married to an Irish citizen for three years and whether the marriage was still intact.
There was no obligation to reside in Ireland to receive an Irish passport under the rule.
It is believed that the Minister for Justice had no role in the granting of citizenship under the rule, which was repealed as part as part of a series of measures introduced to implement citizenship changes required under the Belfast Agreement.
Mr Nafi said: "I was informed by British journalists of certain allegations against me made in the USA in connection with an ongoing case with a Palestinian university professor at the University of South Florida. As far as I know, the American officials who made allegations against me presented no evidence whatsoever."
He added: "I and my family feel absolutely shocked to hear these allegations. I would like to make it absolutely clear that I am not and have never been a member of any organised political group whether in the Middle East or anywhere else."
Ms Nafi, who is a convert to Islam, said her husband was "the innocent one". She added: "I felt like it was not happening and that I will wake up in a couple of days and everyone will have gone away."